ABSTRACT
The energy band structure of the conduction band (energy-momentum relation of electrons) is crucial to understanding the electron transport of crystalline materials. In this paper, we describe an angle-resolved low-energy inverse photoelectron spectroscopy (AR-LEIPS) apparatus that examines the conduction band structures of materials sensitive to the electron beam, such as organic semiconductors and organic-inorganic hybrid perovskites. The principle of this apparatus is based on AR inverse photoelectron spectroscopy. To minimize radiation damage and improve energy resolution, we employed our previous approach used in LEIPS [H. Yoshida, Chem. Phys. Lett. 539-540, 180 (2012)]. We obtained an overall energy resolution of 0.23 eV with a momentum resolution of 0.9 nm-1 at the electron kinetic energy of 2 eV or higher.
ABSTRACT
The conduction band dispersion in methylammonium lead iodide (CH3NH3PbI3) was studied by both angle-resolved two-photon photoelectron spectroscopy (AR-2PPE) with low photon intensity (â¼0.0125 nJ/pulse) and angle-resolved low-energy inverse photoelectron spectroscopy (AR-LEIPS). Clear energy dispersion of the conduction band along the Γ-M direction was first observed by these independent methods under different temperatures, and the dispersion was found to be consistent with band calculation under the cubic phase. The effective mass of the electrons at the Γ point was estimated to be (0.20 ± 0.05)m0 at the temperature of 90 K. The observed conduction band energy was different between the AR-LEIPS and AR-2PPE, which was ascribed to the electronic-correlation-dependent difference of initial and final states probing processes. The present results also indicate that the surface structure in CH3NH3PbI3 provides the cubic-dominated electronic property even at lower temperatures.
